The present invention relates to apparatus for the controlled mixing of two gaseous substances and relates particularly to apparatus for the preparation of mixtures for calibrating analysers for exhaust gases from internal combustion engines.
In order to form a calibration curve for an analyser, it is necessary to feed samples of gaseous mixtures of known composition successively to its input. These samples are obtained by mixing a first gas, termed the zero gas, with a second gas, termed the span gas.
The zero point on the calibration curve can be defined by supplying the analyser with the zero gas while intermediate points and the full scale reading on the calibration scale can be defined by supplying the analyser with mixtures in which the zero gas and the span gas are present in known, increasing proportions.